"We do not copy results from any of our competitors. Period. Full stop," he wrote. "We have some of the best minds in the world at work on search quality and relevance, and for a competitor to accuse any one of these people of such activity is just insulting."

He suggested that any Google claim to the contrary was a mere publicity stunt. It's "interesting to watch the level of protest and feigned outrage from Google," he said.

In fact he had a pop at Google pointing to changes Microsoft had made to Bing over recent months. "If you are keeping tabs, you will notice Google has 'copied' a few of these," he wrote.

Earlier this week Googler Amit Singhal, accused Bing of "cheating" by copying Google results. He outlines his claims here saying that over a few months "we noticed that URLs from Google search results would later appear in Bing with increasing frequency for all kinds of queries: popular queries, rare or unusual queries and misspelled queries. Even search results that we would consider mistakes of our algorithms started showing up on Bing."

Shortly after word of Google's findings spread on Tuesday, executives from Google and Microsoft sniped at each other on stage at the Farsight search conference in San Francisco.

Google based the claim on a series of experiments it conducted in which it modified its search engine to create artificial associations between various search terms and websites that would show up when the terms were entered into the Google search engine."

"Some Bing results increasingly look like an incomplete, stale version of Google results—a cheap imitation," he wrote

Biting back, Mehdi says "Google’s 'experiment' was rigged to manipulate Bing search results through a type of attack also known as 'click fraud'. That’s right, the same type of attack employed by spammers on the web to trick consumers and produce bogus search results.

"What does all this cloak and dagger click fraud prove? Nothing anyone in the industry doesn’t already know. As we have said before and again in this post, we use click stream optionally provided by consumers in an anonymous fashion as one of 1,000 signals to try and determine whether a site might make sense to be in our index. "